Diesel engines are frequently damaged or destroyed by over revving, over heating, or operating with no or low oil pressure. Often diesel engines are operated in remote locations without monitoring by persons, instruments or equipment which would either automatically or manually shut down the engine when a detrimental condition arises. Additionally, diesel engines installed in tractor trailer rigs are frequently damaged or destroyed by operating with no or low oil pressure, in an overheated condition, or over revving. Over revving may occur when a diesel is operated in an atmosphere with high levels of volatile hydrocarbons, which may occur near oil wells, chemical plants, mining, and fuel loading areas. In these areas fugitive volatile hydrocarbons may be drawn into the diesel engine air intake and used as unregulated fuel for the engine which then uncontrollably revs resulting in catastrophic engine failure and possibly explosion. Diesel fuel shut off devices are not effective since the atmosphere is the fuel source via the engine air intake system. Accordingly, air intake shut off devices are employed which are either manually or automatically actuated. With manually operated shut down systems the operator is usually not near the tripping mechanism and the over revving and engine failure usually occurs with such rapidity that manual input is not possible. Automated air intake shut down devices are frequently actuated by electrical components with various sensors for monitoring engine conditions. While these prior art shut down devices which utilize electrical actuators are useful the various electrical components often fail leaving the entire shut down system inoperable. Additionally air intake shut down systems installed on over the road trucks are not able to be deactivated to prevent inadvertent shut down during normal driving conditions. It is also desirable to deactivate the over revving component of the shut down device, for over the road use, while maintaining operation of other shut down parameters, such as oil pressure and water temperature. There is a need for a shut down system to protect a diesel engine from over revving, low oil pressure, high coolant temperature and which may be activated manually, requires no external power supply for operation, and the over revving component may be deactivated or bypassed if desired while retaining the oil pressure and water temperature shut down control. The present invention accomplishes these and other goals by utilizing an air intake shut off valve which is tripped to shut off air flow there through by specific engine parameters including over revving, oil pressure, and coolant temperature. The device utilizes variations in the ratio between the air pressure and vacuum measured in different locations of the air intake of a turbo charged diesel engine during load and no load conditions. During load conditions, such as when the output shaft of the engine is coupled to a load, such as a truck drive train, a pump or some other machinery, a slight vacuum is created between the turbo and air filter, while at the same time between the turbo and the engine, air pressure increases. During no load conditions, such as uncontrolled over revving which occurs when the engine throttle is opened and the engine output is not coupled to a load, vacuum is increased and the amount of air pressure increase is lower. The invention utilizes these disproportionate pressure and vacuum changes to regulate and trip the shut off valve. The device includes a butterfly valve mounted within the engine air intake and between the air cleaner and the turbo charger intake. The valve is moved from an open position to a closed position by a tripping mechanism which is tripped by the movement of a pair of diaphragms which is caused by changes in air pressure and vacuum within the air intake system both upstream and downstream of the turbo charger of the engine. A primary diaphragm moves the tripping mechanism to a closed by the influence of vacuum between the turbo charger and the air filter, while the other diaphragm regulates and counteracts movement of the primary diaphragm by the influence of increased air pressure between the turbo charger and the engine during high revving load conditions. The dual diaphragm system, with one diaphragm regulating the other, assures the shut down device will only operate when the engine is over revving during no load conditions. Other engine parameters are linked to the shut down system by utilizing truck air, created by the onboard truck air pump, which is utilized to influence movement of the diaphragms and valve if oil pressure drops or water temperature increases. The invention includes a system which allows the over revving component of the shut down device to be bypassed or deactivated while maintaining the oil pressure and water temperature controls, which is very useful for over the road truck use. The device may also be retro fitted on DETROIT.TM. diesel engines equipped with a blower to control closing the flapper valve in the same manner.